This invention relates to an improved large scale process for reacting aldehydes and/or ketones with ammonia over an effective zeolitic catalyst to form a mixture of pyridine and/or alkylpyridine(s).
The condensation reaction is well known whereby carbonyl-containing compounds can be reacted with ammonia to form pyridine-type bases, including pyridine and alkylpyridines such as the picolines (alpha, beta and gamma), the lutidines, ethylpyridines, etc., using an amorphous or a zeolitic catalyst. Depending on the choice of aldehydes and/or ketones, the major product can be varied and is determined primarily by the underlying stoichiometry of the reaction, statistical considerations and in the case of zeolitic catalysis by pore size considerations.
However, the product mixture in all cases is a complicated blend of pyridine and the alkylpyridines. Methods have long been sought to improve the controllability of the underlying reaction whereby the relative ratios of products can be better and more easily selected, preferably without loss of total yield. This is especially critical in the case of large scale, continuous systems, e.g., of the pilot plant or full commercial production scale, where it is imperative that any technique for adjusting product composition be implementable without highly expensive and inefficient system shut-down. Very few such techniques exist.
Such ease of controllability would provide a major advantage since the marketplace demand for each product fluctuates periodically. Historically, pyridine has been the major product in view of its use as an intermediate for other industrial products. See, e.g., "Pyridine and Pyridine Derivatives", Goe, Kirk-Othmer, Volume 19, 454-483 (1982), and Golunski et al., Applied Catalysis, 23 (1986), 1-14. However, in recent times, the market has undergone more dramatic changes whereby the relative demand for alkylpyridines has increased, especially for beta-pyridine, e.g., as an intermediate for preparation of niacinamide and other medicinal, agricultural and chemical products. Thus, it is presently especially valuable to have facile, on-line methods for varying the relative yields of pyridine and the various alkylpyridines in a given reaction, without significant loss of total yield. On a commercial scale, losses of even one percent will have major economic repercussions.
Various factors have been noted in the past which affect product composition and yield in one way or another. For example, Grigolet (German Patent 20 51 316) describes the effect of coke levels on the product of the reaction of crotonaldehyde using an amorphous catalyst. The desire is to minimize betapicoline production. On the other hand, Uebel et al. [Chem. Tech. (Leipzig), 22, 679 (1970)] describe the substitution of methylamine for ammonia in the gasphase homocondensation of acrolein to produce lower overall yields and an increase of beta-picoline over pyridine, again using an amorphous catalyst.
Other references are also known wherein variations (intentional or not) in relative or total product yields are achieved over amorphous catalysts. For example, Minato et al. (U.S. Pat. No. 3,946,020) reacts acetaldehyde, formaldehyde and propionaldehyde (Example 2; Reference Example 2). An increased yield of beta-picoline is shown, the relative amounts of other alkylpyridines not being given. British Patent 929,694 also utilizes a reactant combination of formaldehyde, acetaldehyde and propionaldehyde to prepare pyridine and beta-picoline. British Patent 966,264 discusses the employment of formaldehyde with a lower aliphatic ketone and a saturated aliphatic aldehyde to prepare alkylpyridines. JP 61-53266 reacts acrolein, acetaldehyde and formaldehyde. Gamma-picoline yield is lowered without decreasing the yield of pyridine. JP 61-53265 prepares 3,5-lutidine and beta-picoline by reacting acrolein, propionaldehyde and formaldehyde. JP 45-39262 also employs a ternary mixture of reactants (acrolein, acetaldehyde and propionaldehyde) to prepare beta-picoline and pyridine, along with minimum production of gamma-picoline. British Patent 1,141,526 suggests that increasing the amount of acetaldehyde in a binary mixture of formaldehyde and acetaldehyde will decrease the yield of pyridine and beta-picoline while increasing the yield of alpha- and gamma-picoline.
While these references discuss, in an amorphous catalyst system, the effects on product composition of reactant changes, they do so only on a batch system basis and on small scale runs. They do not address the question of how to adjust product compositions on large scale continuous systems, and especially not on such systems employing zeolites as catalysts.
In fact, there is little discussion of useful techniques of varying the relative or total amounts of pyridine and alkylpyridines when a zeolitic catalyst is employed Feitler et al. (U.S. Pat. No. 4,675,410) discloses the use of a zeolite catalyst for the reaction and discusses various methods for improving overall yields and for varying the ratio of pyridine to alkylpyridines. These primarily involve use of a fluidized bed and temperature effects. The table in Column 4 of U.S. Pat. No. 4,675,410 does mention use of a ternary mixture in a reaction using a zeolite catalyst. However, no hint is given as to the expected product yields or any appropriate relative amount of the third component, butyraldehyde, in conjunction with the binary mixture, acetaldehyde and formaldehyde. Only the approximate underlying stoichiometry of the reaction is stated. EP 232,182 also involves the same basic system but requires thallium, lead or cobalt doping to optimize pyridine yield. Older references, e.g., U.S. Pat. No. 4,220,783 (inclusion of methanol or formaldehyde increases selectivity to pyridine) and U.S. Pat. No. 3,728,408, discuss more fundamental aspects of the basic reaction.
Thus, the need still exists for an improved method for varying the relative amounts of pyridine and alkylpyridines in zeolite-catalyzed reactions carried out continuously on large scales, without significantly decreasing overall yield of pyridine-type bases. Primarily, there is a need for increasing the relative amounts of alkylpyridines since most prior work has been directed to optimizing pyridine yields.